This invention relates to bumping structures for making an electrical connection, and more particularly to bumping structures having a flat top and methods of preparing the same.
As the number of users of visual interfaces such as notebooks, video and digital cameras, electronic dictionaries, pagers, personal digital assistants, and visual display units are rapidly increasing, smaller and lighter weight products are required. Liquid crystal display technology is one of the promising technologies for meeting the smaller size and lighter weight requirements of future products. Traditional ways of mounting the driver chips to the liquid crystal display panels including the seal and zipper strip connector methods. Another approach is the tape automatic bonding which has the benefit of handling finer pitch and savings in package size. But the tape carrier package is expensive. Another mounting technology called xe2x80x9cchip on glassxe2x80x9d has emerged as a better and more cost-effective means of mounting driver chips to the liquid crystal display panel with the highest possible packing density.
In the chip on glass technology, one of the more important problems to solve is how to consistently obtain a good connection between the chip anisotropic conductive film and glass substrate. With respect to the bumping process, a flat-top gold bump is one of the best solutions today. However, traditional gold bump processing methods don""t always produce a flat-top surface. Unflat-top bump surfaces do not provide good electrical contact.
FIGS. 1A-E illustrate a prior art method of making a semiconductor device having a bump with a flat engagement surface. FIG. 1A illustrates a method of providing a semiconductor device 10 including a substrate portion 12 having a silicon base portion 14 and connectivity portion 16 including a plurality of alternating inter-level dielectric layers and metallization layer is a manner known to those skilled in the art. One of the metallization layers may provide a bond pad 18 on an upper surface of the substrate 12. A passivation layer 20 such as silicon dioxide, silicon nitride, or silicon oxy-nitride may be provided overlying the substrate and includes an opening 22 therein exposing at least a portion of bond pad 18.
FIG. 1B illustrates a method of providing a photoresist layer 24 having an opening 26 therein and aligned with the bond pad 18 and depositing an under bump metallurgy 28 over the bond pad 18 and through the opening 26. Alternatively, it is known to those skilled in the art to deposit the under bump metallurgy over the entire surface of the substrate and thereafter deposit the first passivation layer 24 so that the opening 26 is still aligned with the bond pad 18.
FIG. 1C illustrates a method of removing the first photoresist layer 24 and depositing a second photoresist layer 30 having an opening 32 therein perfectly aligned with a selected portion of the under bump metallurgy 28 and bond pad 18. When the opening 32 in the second photoresist layer 30 is perfectly aligned with the under bump metallurgy 28, an inner wall 31 of the second photoresist layer 30 defining the opening in 32 is flush with and is in the same plane as an inner wall 29 of the under bump metallurgy 28.
Thereafter, as shown in FIG. 1D, gold 34 is deposited through the opening 32 in the second photoresist layer 30 and onto the under bump metallurgy 28. As shown in FIG. 1E, the second photoresist layer 30 is then removed to produce a bump structure 34 having an upper engagement surface 36 which is flat.
However, as shown in FIG. 2A, the second photoresist layer 30 may be positioned so that the opening 32 is not perfectly aligned with the under bump metallurgy 28 in that the inner wall 31 of the second photoresist layer 30 and the inner wall 29 of the under bump metallurgy 28 are not flush and are not in the same plane. The misalignment can be caused by a number of different manufacturing problems including, for example but not limited to, the opening 32 being too small or too large, or the opening 32 not being aligned or registered properly with the appropriate portions of the underlying under bump metallurgy 28 and bond pad 18. As shown in FIG. 2B, when the gold 34 is electroplated through the opening 32 of the second photoresist layer 30 the gold is deposited in a manner following the topography of the under bump metallurgy 18 including the raised portions 38 that are formed over the portion of the passivation layer 20 covering the bond pad 18. When the second photoresist layer 30 is stripped, a bump structure 34 is provided having an upper surface 36 including raised portions or horns 40. The raised portions or horns 40 of the bump structure 34 do not allow for good electrical contact between the upper surface 36 of the bump structure 34 and another electrical component.
One embodiment of the invention includes a method of making an electrical contact bump structure on a substrate including providing a substrate having a bond pad, and a passivation layer overlying a portion of the substrate and wherein the passivation layer includes an opening therein exposing a portion of the bond pad, and wherein the passivation layer has a raised portion overlying the bond pad. Forming an under bump metallurgy over at least the exposed portion of the bond pad and over at least a portion of the raised portion of the passivation layer overlying the bond pad. Forming a sacrificial blanket having an opening therein that in cross-section has an inverted T-shape over the substrate so that the opening in the sacrificial blanket is aligned with the bond pad. Depositing an electrically conductive material into the opening in the sacrificial blanket so that the electrically conductive material overlies at least a portion of the under bump metallurgy including a portion of the under bump metallurgy overlying the raised portion of the passivation layer and so that a bump structure is formed having a flat-top engagement surface that is free of any raised portion.
Another embodiment of the invention further includes removing the sacrificial blanket.
Another embodiment of the invention further includes etching back any excess portion of the under bump metallurgy using the bump structure as a mask.
In another embodiment of the invention the forming of the sacrificial blanket includes forming a first photoresist layer and forming an opening in the first photoresist layer, forming a second photoresist layer over the first photoresist layer and forming an opening in the second photoresist layer aligned with the opening in the first photoresist layer so that the opening in the first photoresist layer is larger than the opening in the second photoresist layer and so that the opening in the first photoresist layer and the opening in the second photoresist layer together form an opening through the first photoresist layer and second photoresist layer that in cross-section has an inverted T-shape.
In another embodiment of the invention the forming of the sacrificial blanket having an opening therein that in cross-section has an inverted T-shape and over the substrate so that the opening in the sacrificial layer is aligned with the bond pad includes forming a first photoresist layer over the substrate, exposing a portion of the first photoresist layer to ultraviolet light, and forming a second photoresist layer over the first photoresist layer and exposing a portion of the second photoresist layer to ultraviolet light so that the exposed portion of the second photoresist layer smaller than the exposed portion of the first photoresist layer, and removing the exposed portions of the first photoresist layer and the second photoresist layer to provide an opening through the first photoresist layer and the second photoresist layer that in cross-section has an inverted T-shape.
In another embodiment of the invention the forming of the sacrificial layer having an opening therein that in cross-section has an inverted T-shape over the substrate so that the opening in the sacrificial blanket is aligned with the bond pad includes forming a first photoresist layer over the substrate and exposing the first photoresist layer to ultraviolet light without a mask, and forming a second photoresist layer over the first photoresist layer and selectively exposing a portion of the second photoresist layer to ultraviolet light, and removing the exposed portion of the second photoresist layer and removing the exposed portion of the first photoresist layer, and where the removed portions of the first photoresist layer is smaller than the removed portion the first photoresist layers so that an opening is provided through the second photoresist layer and the first photoresist layer that in cross-section has an inverted T-shape.
Another embodiment of the invention includes the forming of the sacrificial blanket having an opening therein that in cross-section has an inverted T-shape over the substrate so that the opening in the sacrificial blanket is aligned with the bond pad includes forming a non-photosensitive layer over the substrate, and forming a photoresist layer over the non-photosensitive layer, exposing a portion of the photoresist layer to ultraviolet light, and developing the photoresist layer and removing a portion of the photoresist layer and removing a portion of a non-photosensitive layer so that the portion removed from the photoresist layer is smaller than portion removed from the non-photosensitive layer and so that an opening is formed through the photoresist layer and the non-photosensitive layer that in cross-section has an inverted T-shape.
In another embodiment of the invention the non-photosensitive layer comprises a polyimide.
In another embodiment of the invention the openings in the photoresist layer and the non-photosensitive layer are formed by etching so as to undercut the non-photosensitive layer.
In another embodiment of the invention the depositing of the electrically conductive material through the sacrificial blanket comprises electroplating.
In another embodiment of the invention the electrically conductive material deposited into the opening through the sacrificial blanket comprises gold.
In another embodiment of the invention the depositing of the gold into the opening through the sacrificial blanket comprises electroplating.
In another embodiment of the invention the substrate comprises a semiconductor wafer.
In another embodiment of the invention the substrate is flexible.
In another embodiment of the invention the substrate is rigid.
In another embodiment of the invention the substrate comprises a ceramic material.
In another embodiment of the invention the substrate comprises an organic material.
In another embodiment of the invention the substrate comprises a composite material.
Another embodiment of the invention includes a method of making an electric contact bump structure on a substrate including providing a substrate having a bond pad, and a passivation layer overlying a portion the substrate and wherein the passivation layer includes an opening therein exposing a portion of the bond pad, and wherein the passivation layer has a raised portion overlying the bond pad, and an under bump metallurgy over at least exposed portion of the bond pad and over at least a portion of the raised portion of the passivation layer overlying the bond pad. Forming a sacrificial layer blanket having an opening therein that in cross-section has an inverted T-shape over the substrate so that the opening in the sacrificial blanket is aligned with the bond pad. Depositing an electrically conductive material into the opening in the sacrificial blanket so that the electrically conductive material overlies at least a portion of the under bump metallurgy including the portion of the under bump metallurgy overlying the raised portion of the passivation layer and wherein the bump structure is formed having a flat-top engagement surface that is free of any raised portion.
Another embodiment of the invention includes a method of making an electrical contact bump structure on a substrate including providing a substrate having a bond pad, and a passivation layer overlying a portion of the substrate and wherein the passivation layer includes an opening therein exposing a portion of the bond pad, and wherein the passivation layer has a raised portion overlying the bond pad. Forming a sacrificial blanket having an opening therethrough that in cross-section has an inverted T-shape over the substrate so that the opening through the sacrificial blanket is aligned with the bond pad. Depositing an under bump metallurgy into the opening through the sacrificial blanket. Depositing an electrically conductive material into the opening through the sacrificial blanket so that the electrically conductive material overlies at least a portion of the under bump metallurgy including a portion of the under bump metallurgy overlying the raised portion of the passivation layer and so that a bump structure is formed having a flat-top engagement surface that is free of any raised portion.
Another embodiment of the invention includes a method of providing a substrate having a bond pad, and a passivation layer overlying a portion of the substrate and wherein the passivation layer includes an opening therein exposing a portion of the bond pad, and wherein the passivation layer has a raised portion overlying the bond pad, and an under bump metallurgy over at least the exposed portion of the bond pad and over at least a portion of the raised portion of the passivation layer overlying the bond pad. Forming a first photoresist layer over the substrate including the passivation layer, the under bump metallurgy and the bond pad. Over exposing a portion of the first photoresist layer using a large proximity gap on a mask aligner. Forming a second photoresist layer over and the first photoresist layer, and under exposing a portion the second photoresist layer. Developing the first photoresist layer and second photoresist layer and removing the exposed portions thereof to provide an opening in the first photoresist layer and the second photoresist layer that has in cross-section inverted T-shape.
Another embodiment of the invention includes a method of providing a substrate having a bond pad, and a passivation layer overlying a portion of the substrate and wherein the passivation layer includes an opening therein exposing a portion bond pad, and wherein the passivation layer has a raised portion overlying the bond pad, and an under bump metallurgy over at least the exposed portion of the bond pad and over at least a portion of the raised portion of the passivation layer overlying the bond pad. Forming a first photoresist layer over the substrate, the passivation layer, and the under bump metallurgy. Exposing the first photoresist layer to ultraviolet light without a mask. Forming a second photoresist layer over the first photoresist layer, and selectively exposing a portion of the second photoresist layer to ultraviolet light. Developing the first photoresist layer and second photoresist layer and etching the first photoresist layer and the second photoresist layer to provide an undercut of the first photoresist layer so that an opening is provided through the first photoresist layer and a second photoresist layer that in cross-section has an inverted T-shape.
Another embodiment of the invention includes a method of providing a substrate having a bond pad, and a passivation layer overlying a portion the substrate and wherein the passivation layer includes an opening therein exposing a portion of the bond pad, and wherein the passivation layer has a raised portion overlying the bond pad, and an under bump metallurgy over at least the exposed portion bond pad and over at least a portion of the raised portion of the passivation layer overlying the bond pad. Forming a non-photosensitive layer over the substrate including the passivation layer and the under bump metallurgy. Forming a photoresist layer over the non-photosensitive layer and exposing a portion of the photoresist layer to ultraviolet light. Developing the photoresist layer and etching the photoresist layer and the non-photosensitive layer with an undercut of the non-photosensitive layer to provide an opening in the photoresist layer and the non-photosensitive layer that in cross-section has an inverted T-shape.
In another embodiment of the invention the non-photosensitive layer comprises a polyimide.
Another embodiment of the invention includes a product including a substrate and a bond pad, a bump structure overlying the bond pad for making electrical connection to another component, the bump structure including a body portion and an upper electrical engagement surface positioned furthest from the substrate, and wherein the engagement surface is flat and free of horns, and at least one wing extending outwardly from the body portion and location below the upper electrical engagement surface and closer to the substrate.
In another embodiment of the invention the product includes a substrate including a semiconductor wafer.
In another embodiment of the invention the to bump structure of the product comprises gold.
In another embodiment of the invention the bond pad of the product comprises aluminum.
In another embodiment of the invention the product further includes an under bump metallurgy interposed between the bond pad and the bump structure.
In another embodiment of the invention the product includes an under bump metallurgy including a first layer comprising TiW and a second layer comprising gold.
These and other embodiments of the present invention will become apparent from the following brief description of the drawings, detailed description of the preferred embodiments, and appended claims and drawings.